A conventional wire harness for use in a vehicle is typically comprise of wires each having a conductor of circular shape in cross-section covered with an insulating material. To establish electrical connections between wires of a wire harness or between wires and vehicle-mounted electrical equipment units, connecting terminals are attached to the conductors of the wires by means of crimping or insulation displacement.
To determine pass/fail of a crimping state or an insulation displacement state of the connecting terminal with the conductor, a method is known which takes advantage of a load pattern that changes with time during an operation of attaching a connecting terminal to a wire (Japanese Unexamined Patent Publications Nos. Sho 63-281071, Hei 10-125437). Based on such a determining method, a quality control system has also been established.
In recent years, with the trend of a complicated installation of wires and a reduction in size of connecting terminals, flat cables have been used in place of the conventional wire harnesses, and new connecting terminals called pierce terminals have been used corresponding to the flat cables.
The flat cable used in place of the wire harness is utilized in a module which is disposed in a narrow space or integrated with a vehicle component such as ceiling, door, and dash board. As shown in FIG. 17, a flat cable 1 has flat conductors 1a arranged in parallel and covered with an insulating material 1b. The conductors 1a are made, for example, of copper, aluminum or the like of 0.15 to 0.2 mm in thickness and approximately 1.5 to 2.5 mm in width Wc. The insulating material 1b is, for example, a polyethylene terephthalate (PET) film of 0.09 mm in thickness, or a less expensive polybuthylene terephthalate (PBT), or the like.
As shown in FIG. 18, a connecting terminal 3 has crimp pieces 3b arranged to opposite to one another on both sides of a substrate 3a and is provided at one end with a female terminal 3c. The substrate 3a is slightly narrower than the conductor 1a in width Wt which is set, for example, in a range of approximately 1.2 to 2.0 mm. FIG. 19 shows a connecting terminal 5 which has a female terminal 5c and crimp pieces 5b alternately arranged on a substrate 5a. 
To connect the connecting terminal 3 to the flat cable 1, the crimp pieces 3b are pierced into a desired conductor 1a at desired positions, and the leading ends of the penetrating crimp pieces 3b are bent inward in an arc shape to hold the desired conductor therebetween. In this way, the connecting terminal 3 is electrically connected to the desired conductor 1a of the flat cable 1.
The flat cable 1 having the connecting terminal 3 connected to the desired conductor 1a in the above manner poses a problem that an electrical connection between the conductor 1a and the crimp pieces 3b is not stable, thus entailing a variation. In addition, with regard to the connection with the flat cable 1 and the connecting terminal 3, no method has been established for determining pass/fail of the connection, although a determination method is established for the conventional connecting terminal. Thus, the provision of a method of determining a connecting state has been desired.